Transmission Loss Variability Associated with Upwelling and Downwelling Off the Southwest Coast of India

  • P.V. Hareesh Kumar Naval Physical & Oceanographic Laboratory, Kochi
  • K.G. Radhakrishnan Naval Physical & Oceanographic Laboratory, Kochi
DOI: https://doi.org/10.14429/dsj.60.570
Keywords: Transmission loss, upwelling process, downwelling process, acoustic propagation model, upslope, propagation, downslope propagation, bathymetry

Abstract

Fine resolution spatial survey carried out off the west coast of India during June and December 2004 was utilised to study the transmission loss (TL) variability associated with the upwelling and downwelling processes in this region. During June, the upwelling was confined to the upper 80 m. Downsloping of isotherms below this depth towards the coast and the occurrence of low saline waters indicated the presence of undercurrent. Between the periods of upwelling and downwelling, temperature and salinity in the surface layers increased by 1-2 oC and 2 PSU, respectively, while at the sub-surface levels, the corresponding increase was ~8 oC and ~0.5 PSU. A range-dependent acoustic propagation model based on parabolic equation method was utilized to compute TL for these two periods. The model was run with a source frequency of 3 kHz kept at 5m depth for different environmental setup, viz. propagation along the constant-depth contour, range-independent and range-dependent environment, and upslope/downslope propagation. The computations revealed significant variability in the TL characteristics between the upwelling and downwelling scenario, though bathymetry and geo-acoustic properties were the same. The analysis also stressed the need of range-dependent acoustic propagation model for realistic prediction of transmission loss variability.

Defence Science Journal, 2010, 60(5), pp.476-482, DOI:http://dx.doi.org/10.14429/dsj.60.570

Author Biographies

P.V. Hareesh Kumar, Naval Physical & Oceanographic Laboratory, Kochi

He has obtained his MSc (Oceanography) and PhD (Marine Science) from University of Science and Technology (CUSAT), Cochin. Presently, he is working as Scientist 'F', Head, Physical Oceanography Division, Naval Physical & Oceanographic Laboratory (NPOL), Kochi. His areas of research interests are: Ocean modeling, air-sea interaction, mixed layer dynamics, thermohaline and current variability, Internal waves, sonar oceanography. He has published 46 papers in national and international journals.

K.G. Radhakrishnan, Naval Physical & Oceanographic Laboratory, Kochi

He has obtained his MSc (Oceanography) and PhD (Marine Science) from CUSAT. Presently, he is working as Scientist 'F', Ocean Acoustic Division, NPOL, Kochi. His areas of research interests are: Underwater acoustic propagation, development of sonar range prediction models, influence of various oceanographic features on acoustic propagation, planning and conducting integrated oceanographic and acoustic experiments at sea. He has published 18 papers in national and international journals/symposia.

Published
2010-08-24
How to Cite
Kumar, P., & Radhakrishnan, K. (2010). Transmission Loss Variability Associated with Upwelling and Downwelling Off the Southwest Coast of India. Defence Science Journal, 60(5), 476-482. https://doi.org/10.14429/dsj.60.570
Issue
Vol 60 No 5
Section
Research Papers
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